The present invention relates to a fuel injection valve and, more particularly, to an electromagnetic fuel injection valve which is adapted to stably maintain performance for a long period of time.
Conventional fuel injection valves, as disclosed in A. M. Kiwior U.S. Pat. No. 4,057,190, are formed with a core and a plunger disposed in a body, a fuel passage communicated with a hollow valve chamber, a ball valve secured to the end of the plunger and associated separably with a seat member, and a solenoid coil. When the solenoid coil is energized, the ball valve is opened to eject fuel. Even if a valve shaft is coincident to the axial core of a seat surface as mounted initially in an internal combustion engine, the axial core is slightly displaced during use, irregularly worn, and a fuel leakage phenomenon occurs. When the plunger which reciprocates does not always maintain magnetic flux density in the section constant when the solenoid is energized to flow magnetic flux therethrough. Accordingly, the plunger which reciprocates by the energization of the solenoid cannot accurately move on the axial center, and this causes the irregular wear on the seat surface to be increased, and the stable operation to be lost. Further, since the plunger is restricted in its stroke at the upstream side of the fuel passage which is largely isolated from the seat surface, the plunger is affected by the influence of the deformation by the temperature when an internal combustion engine is operated, and the stroke of the plunger increases in its error due to the superposition of the inclination or displacement of the plunger in the guide pipe due to the presence of a clearance between the plunger and the guide pipe and the above-described thermal deformation of the plunger.